<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE html
          PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
          "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
   <meta name="AUTHOR" content="pme@gcc.gnu.org (Phil Edwards)" />
   <meta name="KEYWORDS" content="libstdc++, libstdc++-v3, GCC, g++, STL, SGI" />
   <meta name="DESCRIPTION" content="SGI extensions preserved in libstdc++-v3." />
   <meta name="GENERATOR" content="vi and eight fingers" />
   <title>SGI extensions to the library in libstdc++-v3</title>
<link rel="StyleSheet" href="../lib3styles.css" />
</head>
<body>

<h1 class="centered"><a name="top">SGI extensions to the library in
libstdc++-v3</a></h1>

<p>This page describes the extensions that SGI made to their version of the
   STL subset of the Standard C++ Library.  For a time we
   <a href="../faq/index.html#5_3">tracked and imported changes and updates
   from most of the SGI STL</a>, up through their (apparently) final release.
   Their extensions were mostly preserved.
</p>

<p>They are listed according to the chapters of the library that they
   extend (see <a href="../documentation.html#3">the chapter-specific notes</a>
   for a description).  Not every chapter may have extensions, and the
   extensions may come and go.  Also, this page is incomplete because the
   author is pressed for time.  Check back often; the latest change was on
   $Date: 2004/12/24 22:40:49 $ (UTC).
</p>

<p>Descriptions range from the scanty to the verbose.  You should also check
   the <a href="../documentation.html#4">generated documentation</a> for notes
   and comments, especially for entries marked with '*'.  For more complete
   doumentation, see the SGI website.  For <em>really</em> complete
   documentation, buy a copy of Matt Austern's book.  *grin*
</p>

<p>Back to the <a href="howto.html">libstdc++-v3 extensions</a>.
</p>


<!-- ####################################################### -->
<hr />
<h3><a name="ch20">Chapter 20</a></h3>
<p>The &lt;functional&gt; header contains many additional functors and
   helper functions, extending section 20.3.  They are implemented in the
   file stl_function.h:
</p>
<ul>
  <li><code>identity_element</code> for addition and multiplication. * </li>
  <li>The functor <code>identity</code>, whose <code>operator()</code>
      returns the argument unchanged. * </li>
  <li>Composition functors <code>unary_function</code> and
      <code>binary_function</code>, and their helpers <code>compose1</code>
      and <code>compose2</code>. * </li>
  <li><code>select1st</code> and <code>select2nd</code>, to strip pairs. * </li>
  <li><code>project1st</code> and <code>project2nd</code>. * </li>
  <li>A set of functors/functions which always return the same result.  They
      are <code>constant_void_fun</code>, <code>constant_binary_fun</code>,
      <code>constant_unary_fun</code>, <code>constant0</code>,
      <code>constant1</code>, and <code>constant2</code>. * </li>
  <li>The class <code>subtractive_rng</code>. * </li>
  <li>mem_fun adaptor helpers <code>mem_fun1</code> and
      <code>mem_fun1_ref</code> are provided for backwards compatibility. </li>
</ul>
<p>20.4.1 can use several different allocators; they are described on the
   main extensions page.
</p>
<p>20.4.3 is extended with a special version of
   <code>get_temporary_buffer</code> taking a second argument.  The argument
   is a pointer, which is ignored, but can be used to specify the template
   type (instead of using explicit function template arguments like the
   standard version does).  That is, in addition to
</p>
   <pre>
   get_temporary_buffer&lt;int&gt;(5);</pre>
   you can also use
   <pre>
   get_temporary_buffer(5, (int*)0);</pre>
<p>A class <code>temporary_buffer</code> is given in stl_tempbuf.h. *
</p>
<p>The specialized algorithms of section 20.4.4 are extended with
   <code>uninitialized_copy_n</code>. *
</p>
<p>Return <a href="howto.html">to the main extensions page</a> or
   <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>


<hr />
<h3><a name="ch23">Chapter 23</a></h3>
<p>A few extensions and nods to backwards-compatibility have been made with
   containers.  Those dealing with older SGI-style allocators are dealt with
   elsewhere.  The remaining ones all deal with bits:
</p>
<p>The old pre-standard <code>bit_vector</code> class is present for
   backwards compatibility.  It is simply a typedef for the
   <code>vector&lt;bool&gt;</code> specialization.
</p>
<p>The <code>bitset</code> class has a number of extensions, described in the
   rest of this item.  First, we'll mention that this implementation of
   <code>bitset&lt;N&gt;</code> is specialized for cases where N number of
   bits will fit into a single word of storage.  If your choice of N is
   within that range (&lt;=32 on i686-pc-linux-gnu, for example), then all
   of the operations will be faster.
</p>
<p>There are
   versions of single-bit test, set, reset, and flip member functions which
   do no range-checking.  If we call them member functions of an instantiation
   of &quot;bitset&lt;N&gt;,&quot; then their names and signatures are:
</p>
   <pre>
   bitset&lt;N&gt;&amp;   _Unchecked_set   (size_t pos);
   bitset&lt;N&gt;&amp;   _Unchecked_set   (size_t pos, int val);
   bitset&lt;N&gt;&amp;   _Unchecked_reset (size_t pos);
   bitset&lt;N&gt;&amp;   _Unchecked_flip  (size_t pos);
   bool         _Unchecked_test  (size_t pos);</pre>
<p>Note that these may in fact be removed in the future, although we have
   no present plans to do so (and there doesn't seem to be any immediate
   reason to).
</p>
<p>The semantics of member function <code>operator[]</code> are not specified 
   in the C++ standard.  A long-standing defect report calls for sensible
   obvious semantics, which are already implemented here:  <code>op[]</code>
   on a const bitset returns a bool, and for a non-const bitset returns a
   <code>reference</code> (a nested type).  However, this implementation does
   no range-checking on the index argument, which is in keeping with other
   containers' <code>op[]</code> requirements.  The defect report's proposed
   resolution calls for range-checking to be done.  We'll just wait and see...
</p>
<p>Finally, two additional searching functions have been added.  They return
   the index of the first &quot;on&quot; bit, and the index of the first
   &quot;on&quot; bit that is after <code>prev</code>, respectively:
</p>
   <pre>
   size_t _Find_first() const;
   size_t _Find_next (size_t prev) const;</pre>
<p>The same caveat given for the _Unchecked_* functions applies here also.
</p>
<p>Return <a href="howto.html">to the main extensions page</a> or
   <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>


<hr />
<h3><a name="ch24">Chapter 24</a></h3>
<p>24.3.2 describes <code>struct iterator</code>, which didn't exist in the
   original HP STL implementation (the language wasn't rich enough at the
   time).  For backwards compatibility, base classes are provided which
   declare the same nested typedefs:
</p>
   <ul>
    <li>input_iterator</li>
    <li>output_iterator</li>
    <li>forward_iterator</li>
    <li>bidirectional_iterator</li>
    <li>random_access_iterator</li>
   </ul>
<p>24.3.4 describes iterator operation <code>distance</code>, which takes
   two iterators and returns a result.  It is extended by another signature
   which takes two iterators and a reference to a result.  The result is
   modified, and the function returns nothing.
</p>
<p>Return <a href="howto.html">to the main extensions page</a> or
   <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>


<hr />
<h3><a name="ch25">Chapter 25</a></h3>
<p>25.1.6 (count, count_if) is extended with two more versions of count
   and count_if.  The standard versions return their results.  The
   additional signatures return void, but take a final parameter by
   reference to which they assign their results, e.g.,
</p>
   <pre>
   void count (first, last, value, n);</pre>
<p>25.2 (mutating algorithms) is extended with two families of signatures,
   random_sample and random_sample_n.
</p>
<p>25.2.1 (copy) is extended with
</p>
   <pre>
   copy_n (_InputIter first, _Size count, _OutputIter result);</pre>
<p>which copies the first 'count' elements at 'first' into 'result'.
</p>
<p>25.3 (sorting 'n' heaps 'n' stuff) is extended with some helper
   predicates.  Look in the doxygen-generated pages for notes on these.
</p>
   <ul>
    <li><code>is_heap</code> tests whether or not a range is a heap.</li>
    <li><code>is_sorted</code> tests whether or not a range is sorted in
        nondescending order.</li>
   </ul>
<p>25.3.8 (lexigraphical_compare) is extended with
</p>
   <pre>
   lexicographical_compare_3way(_InputIter1 first1, _InputIter1 last1,
                                 _InputIter2 first2, _InputIter2 last2)</pre>
<p>which does... what?
</p>
<p>Return <a href="howto.html">to the main extensions page</a> or
   <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>


<hr />
<h3><a name="ch26">Chapter 26</a></h3>
<p>26.4, the generalized numeric operations such as accumulate, are extended
   with the following functions:
</p>
   <pre>
   power (x, n);
   power (x, n, moniod_operation);</pre>
<p>Returns, in FORTRAN syntax, &quot;x ** n&quot; where n&gt;=0.  In the
   case of n == 0, returns the <a href="#ch20">identity element</a> for the
   monoid operation.  The two-argument signature uses multiplication (for
   a true &quot;power&quot; implementation), but addition is supported as well.
   The operation functor must be associative.
</p>
<p>The <code>iota</code> function wins the award for Extension With the
   Coolest Name.  It &quot;assigns sequentially increasing values to a range.
   That is, it assigns value to *first, value + 1 to *(first + 1) and so
   on.&quot;  Quoted from SGI documentation.
</p>
   <pre>
   void iota(_ForwardIter first, _ForwardIter last, _Tp value);</pre>
<p>Return <a href="howto.html">to the main extensions page</a> or
   <a href="http://gcc.gnu.org/libstdc++/">to the homepage</a>.
</p>


<!-- ####################################################### -->

<hr />
<p class="fineprint"><em>
See <a href="../17_intro/license.html">license.html</a> for copying conditions.
Comments and suggestions are welcome, and may be sent to
<a href="mailto:libstdc++@gcc.gnu.org">the libstdc++ mailing list</a>.
</em></p>


</body>
</html>
